let a = 7
let b = 52

function fn1(arg1:any,arg2:any) {
    return arg1 + arg2
}

function fn2(this:object) {
    console.log(this)
}


// "strictNullChecks": true时，就会提示box1对象可能为null,此时我们可以做一些判断
let box1 = document.getElementById("box1")
box1?.addEventListener("click",function() {
    console.log("点击事件......")
})